Known internal combustion engines for vehicles comprise a head bearing one or more cylinders, inside which the engine cycle is carried out, and which communicate with respective combustion chambers of the engine. On the aforesaid head there are also provided suitable seats for connecting the combustion chamber with ducts suitable for supplying said chamber with a mixture of unburnt fuel and air (“intake ducts”) and for removing the combusted gases from said combustion chamber (“exhaust ducts”).
The flows from and towards each combustion chamber are controlled by suitable valves acting on the aforementioned seats. In particular, each valve essentially comprises a guide element, fixed inside a cavity of the head of the engine and defining a through seat, and a stem, slidingly movable in opposite directions within the aforesaid seat and carrying at one end a shuttering element to close the connection between the relative intake or exhaust duct and the corresponding combustion chamber.
The opposite end of the valve stem axially projects from the respective guide element and receives actuating forces from a relative control device, for example a cam shaft.
The valve stem is axially loaded by a helical spring in the closing direction of the connection between the respective intake or exhaust duct and the corresponding combustion chamber.
In particular, the spring is coaxially mounted about the valve and is axially interposed between a stationary surface formed on the head of the engine and a plate fastened to the valve stem, near or at the end of the stem cooperating with the control device.
The valves of the aforesaid type normally have sealing gaskets for the lubricating oil normally circulating in the engines. Said gaskets, in one of the most commonly known forms, comprise a support or reinforcement member, having a substantially tubular shape and made of a single piece of metal material, and an annular sealing element, made of elastomeric material and interposed between the support element and the valve.
In particular, the sealing element typically comprises a first portion cooperating through its own radially inner annular surface with the radially outer annular surface of the portion of the guide element oriented in use towards the aforementioned control device, and a second portion cooperating directly with the valve stem.
The gaskets of the aforesaid type are widely used on all internal combustion engines to control the amount of lubricating oil flowing from the distribution area to the combustion chambers. An excessive flow of lubricating oil causes, besides an obviously high consumption of the oil, a deterioration of the efficiency of the engine and a reduction in the performance of the catalyst of the vehicle. On the other hand, an insufficient flow causes increased wear and noise of the valves together with local temperature peaks. These phenomena can cause a premature damage to the valves due to the seizure of the valve stem inside the guide element.
Thanks to the first portion of the sealing element acting on the guide element of the relative valve, the known sealing gaskets allow a static type seal, and thanks to the second portion of the sealing element cooperating with the stem, a dynamic type seal. In particular, the static seal must ensure a certain degree of radial compression on the guide element in order to avoid the leakage of lubricating oil towards the combustion chambers and at the same time keep the gasket in position, while the dynamic seal is designed for allowing the minimum flow of oil necessary for the lubrication of the coupling between the stem and the guide element.
The support element includes:                a substantially cylindrical main portion;        a first annular flange extending radially inwardly from an axial end of the main portion and partly embedded in an annular seat of the sealing element; and        a second annular flange extending radially outwardly from an opposite axial end of the main portion and suitable to be pushed against the aforementioned stationary surface of the head of the motor by the spring acting on the valve stem.        
In practice, the second annular flange of the support element defines an abutment surface for an axial end of the spring and receives from this latter the normal operating loads.
The second annular flange also allows the gasket to be actuated in the desired position on the valve.
In order to reduce the weight and costs of the gaskets described above, the patent application EP-B-2868875 proposes the implementation of the support element in two separate snap coupled components. The component directly cooperating with the sealing element and therefore radially innermost was made of metal material, while the component cooperating with the valve spring and therefore radially outermost was made of plastic material.
In practice, the radially innermost component defines an interaction portion of the support element with the sealing member, while the radially outermost component defines a positioning portion of the support element on the head of the engine and with respect to the valve guide element.
In more detail, the radially outermost component essentially comprises a cylindrical main body, adapted to define a receiving seat for an axial end portion of the radially innermost component, and a flat annular end flange, radially projecting outwardly from the main body and adapted to abuttingly cooperate against the aforementioned stationary surface of the head of the engine under the axial thrust of the valve spring.
The radially outermost component further comprises three hooking projections projecting from an end edge of the main body opposite the annular flange cooperating with the head of the engine; the aforesaid hooking projections extend, in an undeformed position, in a direction parallel to the axis of the gasket, and are angularly equidistant about the aforesaid axis and elastically flexible from and towards the radially innermost component for hooking or releasing it.
In particular, each hooking projection carries at its free end a tooth adapted to snap couple with an axial end portion of the radially innermost component opposite the one housed in the seat of the main body of the radially outermost component.
The solution described, although functionally valid, is susceptible of further improvements. In fact, it has been noted that, in the case of high pressures in the engine, the radially innermost component, and the sealing element with it, could be pushed towards the end teeth of the hooking projections with a high force capable of spreading open the hooking projections and consequently of removing the gasket from the respective valve.